The present invention relates to an improved precast concrete slab and a method of making the same.
In reinforced-concrete constructions, concrete is conventionally mixed with water at construction sites, and this process can easily cause dust pollution. Precast concrete slabs are later adopted for forming walls or floors in constructions to reduce dust pollution and to speed up the construction work. But because concrete has a specific weight as high as 2.4 and it easily becomes brittle, when these precast concrete slabs are used in the construction of precast steel buildings, they will cause certain drawbacks:
(1) At present, precast concrete wall slabs or floor slabs in steel buildings weigh as much as several tons a piece and must be mounted in place one by one by means of giant cranes. Using giant cranes in construction work entails high cost and causes noise pollution, and in constructing tall buildings, it is very inconvenient.
(2) To maintain a certain degree of strength, a concrete slab must be very thick; hence, the utilizable space of the upper floors of a tall building becomes less owing to the comparatively greater thickness of the concrete wall slabs used.
(3) In order to support the weight of such bulky wall slabs and floor slabs, a greater load must be taken into consideration when designing the steel skeleton structure of a building; consequently, the steel used must be thicker, and the total weight of the amount of steel required for the whole building is considerable.
(4) The weight of so many tall buildings has an adverse effect on the land.
In regard to the above-mentioned drawbacks in conventional concrete slabs, a prior art sandwich type three-ply concrete slab is an improvement thereon. With reference to FIG. 1, inorganic fibers, cement, and plaster are mixed and pressed to form outer layers 10; then the space between two outer layers 10 is filled with cement and expandable beads such as PU and PE to form the middle layer 11. To enable two adjacent slabs thus formed to couple with each other to form an even plane surface, a notch 12 and a flange are respectively provided in the edges of the middle filler layer.
Although the aforementioned prior art is an improvement on conventional reinforced concrete slabs in terms of weight, fire-proof, sound-proof, and heat insulation, the coupling of two adjacent three-ply slabs is achieved by means of the notch 12 and the flange 13 provided in the middle filler layer, which is the weakest part of the slab. Although such a three-ply slab is comparatively lighter, it is still very bulky, and when using cranes in hoisting or mounting a slab, the flange of the slab is vulnerable to damage, which may affect the proper coupling of two adjacent slabs. Furthermore, the three-ply slab is not integrally formed; therefore, each layer may become detached from each other as time goes by. In addition, because the middle layer is formed of expandable materials, its physical strength is insufficient; hence, further improvement is necessary.
There is also a kind of plaster wall slab used in constructions. It consists chiefly of plaster, which is mixed with asbestos fibers, binding agents, and other fiber materials. But because the plaster slab comprises largely of hollow fibers, its physical strength is very weak. Moreover, it will easily mold if water penetrates into it, since the water moisture inside it cannot easily evaporate.